Biomechanical Comparison of Impaction Techniques and Cross-Sectional Femoral Stem Shapes for Cementless Total Hip Arthroplasty.

Introduction: Traditional mallet broaching and stem seating in cementless total hip arthroplasty (THA) can result in femoral stem misalignment, potentially reducing implant longevity. This study aimed to compare the pullout strength of cementless THA femoral stems with different cross-sectional designs achieved through the powered impactor method versus the traditional mallet method.

Methods: The authors utilized 24 polyurethane foam femurs and two femoral bone preservation stems with different proximal cross-sectional shapes (double taper: ACTIS^®, size 5; flat taper: TRI-LOCK^®, size 5). A single orthopedic surgeon broached each femur from size 0 to size 5 using either the powered impactor or mallet impaction methods. Broaching time and component implantation times were recorded. A load-to-failure pullout strength test was conducted, and the ultimate pullout load was recorded.

Results: The broaching time for the TRI-LOCK^® stem showed a statistically significant difference between the two impaction methods (powered: 37±7 seconds, mallet: 75±29 seconds, F[3, 20] = 4.56, p = 0.002), but no statistically significant difference was detected for the ACTIS^® stem between the two impaction methods (powered: 47±22 seconds, mallet: 59±9 seconds, F[3, 20] = 4.56, p = 0.304). There was a statistically significant difference in pullout strength between the two impaction groups, and this strength was influenced by the implant cross-sectional shape (ACTIS^®: 774±75N versus 679±22N, F(3,20) = 16.38, p = 0.018; TRI-LOCK^®: 616±57N versus 859±85N, F(3, 20) = 16.38, p <0.001).

Conclusions: The technique used for femoral bone preparation (powered impactor versus mallet) and the cross-sectional design of the cementless femoral stem are crucial factors that affect initial stem stability and operation time.